Short range radio data transmission systems often use E-H field type tuned loop antennae. Such loop antennae are usually very small in size and have to fit into very small spaces (e.g. remote car alarm keys).
A normal H-field loop antenna consists of a metallic loop conductor and a tuning capacitor at its ends. The form of the loop itself is of secondary importance and known loops have different physical shapes such as rectangular or diamond etc. The tuning capacitance is typically placed in the centre of the loop but can equally be displaced from it.
The use of a tuning capacitor with an H-field loop antenna has a series of significant drawbacks. For example, in an environment where hand held equipment is used, such as a remote car alarm key, human body capacitance can significantly de-tune the resonant frequency of the loop antenna at the capacitance intersection.
Furthermore the requirement for a discrete capacitor component adds to the cost of the loop antenna and the complexity of the design.
This invention seeks to provide a loop antenna which mitigates the above mentioned disadvantages.